I always loved the idea of a codex (not only creature codex) as long as it serves as a suplementary role, not basically an introduction to a world (as it was done eg. in Pillars of Eternity). I think Dragon Age, Mass Effect or The Witcher 3 did the Codex right, even if each did it a bit differently.
To be honest, currently the inspect button is practically useless, or at least seriously underdeveloped. I'd love to see it as a means to read a more detailed lore info, a much longer flavour text about items, creatures etc. All those details could also go into one Codex for convenience. To spice things even more, it would be great if this additional info could be get after successful roll (eg. History or Arcana), of type depending of the inspected target.
Another thing that bothers me in Larian games in general (not only BG3) are lackluster books. They are often very short, containing only necessary info, without any interesting world details. It doesn't need to be as long as often was in TES games, but something akin BG1/BG2 (which IMO is still the best execution of lorebooks I've seen) would be perfect. And of course all books could be neatly categorized in Codex (so you could read them even after selling the book).
